CHEMISTRY COMMUNITY

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extensive properties are dependent on the mass or amount of the substance, they are subject to change. Intensive properties, on the other hand, are independent of mass or amount and are constant for a given substance.

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The side where there is no solid electrode has platinum.

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When two first-order reactants affect the rate constant or when one second-order reactant

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Kc is used when you are given concentrations, and Kp is used when you are given partial pressures of gases. When Kp is given, the products and reactants are both gases. When Kc is given, the products and reactants can consist of gases or aqueous solutions

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Cathode is where reduction occurs, and the anode is where oxidation occurs.

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K’ is the rate of the reverse reaction. kr is the rate constant of the reaction

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The slow step is considered the rate determining step. That means that the rate of the entire reaction is determined by that step. Imagine you are walking up a hill as a group, the slowest member of the group is the rate determining step

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The rate is very high when the reaction starts and decreases as the reaction continues. This can be determined by the slope of the tangent line at that point of the curve

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K is a ratio of products to reactants. Ratios do not have units

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We could have either situation in an exam. The slow step will always be given to you

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If it wasn't a neutral salt, it would not allow for the charges to be balanced.

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Galvanic cells and voltaic cells are the same thing. They both generate electrical energy from chemical energy. Electrolytic cells are the opposite.

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The reducing agent will be the one with the more negative Eo values. the other one will be the oxidizing agent

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The anode is where there is a loss of electrons and the compound is oxidized. The cathode is where there is a gain of electrons and the compound is reduced. You can tell which is more likely by looking at the Eo values. the more negative one is a stronger reducing agent and is therefore more likely ...

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K is when the reaction is at equilibrium. Q is at any other point in the reaction

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A half reaction is balanced when the number of electrons gained during reduction are equal to the number of electrons lost during oxidation

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Half reactions are balanced when there is no net gain or loss of electrons in the total reaction i.e. the number of electrons gained in reduction is equal to the number of electrons lost in oxidation.

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Basic solutions consist of a greater number of OH- ions, therefore, you need to balance the equation using OH- ions.

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A conjugate acid differs from its species by one H+ (ie it has one more H+ than the original species. A conjugate base, on the other hand, has one less proton than its original species.

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A single line indicates direct contact/interaction between two states of matter/ substances. The double line, on the other hand, represents the salt bridge

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the order of a cell diagram is Anode(solid|gas| liquid )|| Cathode (liquid| gas| solid). the solid here is the electrode. if you are not told that any of the elements are solid, you assume the electrode to be an inert Pt electrode. If you follow this outline, you should have no problems with cell di...

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It depends on the oxidation number of the element. If there is an increase in the oxidation number, oxidation is occurring. If there is a decrease in the oxidation number, reduction is occurring. Other, more obvious things to look out for include the gain or loss of protons and oxygen.

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You would use this when given equilibrium constants for two different temperatures and a standard change in enthalpy

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The second law of thermodynamics states that the total entropy of a system always increases for a favourable reaction. That is the system always moves to a state of increased disorder

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This is because ions are charged particle formed as a result of the loss or gain of electrons that affect their oxidation number

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G naught is explicitly for elements in their standard state.

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It wouldn’t mention the term pH in that case. It would explicitly mention initial H+ ion concentration

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W is degeneracy. It is equal to the number of states raised to the number of species

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Spontaneous processes have an increase in entropy. Delta H will be negative and S will be positive. Therefore G will be negative and hence the process is spontaneous

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Heat capacity is a state function as the method to attain the heat capacity of a system is the sum of each component part of the system

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An increase in entropy leads to a decrease in Gibbs free energy. Both these situations represent a spontaneous reaction

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If a system is well insulated enough, it can be considered to be isolated ie there is no transfer of heat or energy

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Closed systems are those that can exchange energy not matter with the surroundings. Isolated systems, on the other hand, can exchange neither with the surroundings. Examples of a closed system include a sealed container (that is capable of transmitting heat etc.), and examples of an isolated system ...

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reversible means that even if there is an infinitesimal change in the system, there will be a significant change in the behavior of the system. the definitions of reversible in equilibrium reactions and thermodynamically, however, differ greatly.

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Enthalpy is the total amount of heat within a system.

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it is taken into account when energy is first required to change the state of matter and then heat the new phase. therefore for example the heating of water from ice takes into account the energy required to melt the ice and then raise the temperature of water.

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The conversion from a double bond to a single bond is a new bond being formed. for organic compounds for example it could be a C-H bond forming. the bond enthalpies of C=O and C-O + C-H are different.

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Enthalpy change of formation is the energy of reactants and products in their most stable state. Enthalpy change of reaction is the difference in those enthalpies

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enthalpies of different reactions can be added together to get the total enthalpy of the system in its change from reactants to products

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if the Ka value is high, or the pKa value is low, the acid is generally a strong acid and vice versa for a weak acid. this is also true for Kb and bases

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the total enthalpy of the system remains the same regardless of the route taken to reach the final product. this is important when the reaction from reactants to products in one step is energetically or chemically unfavorable

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according to le chatelier's principle, a system works to minimize the effect of the change. therefore there will be an increase in the rate of the reverse reaction, and there will be H2 formed until it reached the required level

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For an ICE box problem, the change would always be subtracted on the reactants side and added on the products side.

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Q is the composition of a system at any time (even those other than equilibrium). It is an important indicator that tells you whether equilibrium lies in favor of products or reactants. when Q < K, the reaction will move toward the products, and if Q > K, the reaction will move towards the reactants...

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the Kw of water remains constant at a given temperature, although the concentrations of hydronium and hydroxide ions can vary. for example, in an acidic solution if [H3O+] is say 1.00 x 10^-2, then using the Kw, we can conclude that the [OH-] is 1.00 x 10^ -12.

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PV= nRT is used for ideal gases only. if concentrations and Kp are given, this equation can be used to calculate the partial pressure of products and reactants and vice versa, if partial pressures are given, concentrations can be calculated using this method

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K does not have units as it is a constant value of the ratio of concentrations of products to reactants.

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the H2 molecule has been omitted from the right side of the equation. if it were present, the number of molecules would be the same on the right and the left of the equation, therefore, there'd be no change in equilibrium as a result of a change in pressure.

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find moles of OH- ions in 2ml of 0.175M KOH. Divide this value to obtain concentration of OH- ions. use the formula of pOH to calculate the pOH of solution and then subtract by 14 to calculate the pH

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Inert gases generally do not react, therefore, it is unlikely that their presence will change the reaction mixture at all.

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the stochiometric coefficients show the number of molecules of one type reacting together. therefore, if the equation is 2H20----> H3O+ + OH-, two water molecules react to give one H3O+ molecule and one OH- molecule. concentrations of products are multiplied and divided by reactants to the give the ...

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The concentrations of H3O+ and OH- are equal in water. therefore, using the new value of Kw as 2.1x10^-14, square root it to get concentrations of H3O+ and OH-

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The ICE box is used for concentrations to calculate the concentration of reactants and products at equilibrium given a Kc value. If there is a Kp value given, then pressure in the units atm will be used.

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The -ate is only added for a negatively charged ion. For neutral and positively charged ion, just the metal name is required

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NO2- is nitro and ONO is nitrito

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It means a formal charge of 0 on most atoms.

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Acid-Base titrations are the only ones that we need to know as of now. Other examples are red-ox titration

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To find a hybrid orbital, look at the number of regions of electron density around the atom. If there are 2, the hybridisation will be sp, if there are 3, sp2, 4 = sp3, 5= sp3d, 6=sp3d2

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This is because of the orientation of the lone pairs of electrons in water. Only one can have the correct orientation to bond.

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This is because the formal charge of the second structure is lower due to the presence of resonant structures.

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Something can be a chelating compound when it forms a ring with the metal being a part of it. The answer to your question is the one where the NH3's are closest to each other.

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BF3 is a lewis acid because it is electron deficient and has empty orbitals. Therefore it is an electron acceptor.

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You should know at least some common acids such as hydrochloric acid, sulphuric acid as strong acids, and acetic acid as a weak acid. You should be alright if you're familiar with the examples he went over in lecture. You can tell a base is a strong base if it dissociates completely in solution to f...

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For hybridization, you are just mixing orbitals, to form new orbitals with different shape, size and energy than the component orbitals. This is energetically favorable for the formation of bonds and therefore explains why atoms such as carbon form 4 covalent bonds.

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The definition of an acid varies in both cases. Bronsted focuses on protons. A Bronsted acid is therefore a proton donor. However, Lewis focuses on electrons, and a lewis acid is an electron acceptor.

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This depends on whether the atom has one or two lone pairs, in addition to its two bond pairs. If it has one lone pair, the bond angle will be < 120 degrees, however, if it has two lone pairs, it will have a bond angle << 109.5 degrees (ex. Water has a bond angle of approx. 104.5 degrees)

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No, you can look at the position of the atom on the periodic table and see how many electrons it needs to gain or lose to attain the electronic configuration of the closest noble gas. You will need to make sure that this is energetically favorable. Ex. A sodium atom would rather lose one electron th...

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A coordination compound is one that contains a coordination complex within it. It is when the anions are bonded to the metal via coordinate covalent bonds,where both electrons are donated via the metal atom.

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Yes, all molecules regardless of their polarity or non-polarity experience Van Der Waals interactions due to shift in the electron cloud density. The order of interaction from strongest to weakest is ion-dipole, dipole-dipole, dipole-induced dipole, induced dipole-induced dipole.

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An example for a Van der Waals interaction would be between N2 molecules. They do not have an inherent dipole moment beween the two atoms as they are identical, however, there is an instantaneous dipole created due to a shift in the electron density distribution, which thereby induces a dipole momen...

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CCl4 is a non-polar molecule as the dipole moments of each of the C-Cl bonds cancel each other out, as they are in exactly opposite directions. However, for the molecule CCl3F, there will be a dipole moment generated in the direction of the fluorine atom, due to its high electronegativity. Bond angl...

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Although while naming the molecule, the lone pairs of electrons do not matter, they do influence the molecular geometry of the molecule, and thus change bond angles due to their presence or absence. Each lone pair of electrons represents one region of electron density.

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We can consider any of the carbon atoms to be the central atom in this case, and look at the regions of electron density around each one individually. This will also determine the bond angles in each part of the hydrocarbon.

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The shape of the molecule determines the bond strength as a more branched structure (such as 2,2- dimethylpropane) have smaller surface areas. As the intermolecular attractive forces are determined by this, the forces as stronger. Whereas for straight molecules, it is the opposite.

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This is because the charges on both the atoms are different i.e. one is positive and the other is negative. When using the equation to calculate Ep, you are multiplying both the charges on the atoms (q1.q2/r^2). Since multiplying a negative by a positive, will always give you a negative answer, Ep i...

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All molecules generally possess Van Der Waals forces due to the varying electron density distribution that occurs as a result of the electron cloud moving which temporarily creates a dipole, which can then induce other surrounding molecules to form dipole moments in them.

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This is due to the high electronegativity of the elements N, O and F. This results in a partial negative charge that attracts hydrogen which has a partial positive charge. It is also due to the lone pairs of electrons present around these atoms in a covalent bond.

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High polarizability and high polarizing power are when the electrons in an ionic bond can be distorted. This distortion is a result of the positively charged cation attracting negatively charged electrons. As this resembles the shared characteristic that electrons in a covalent bond face, it is cons...

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The one with the lowest energy will always be correct so it safer to draw that and all it’s resonant structures.

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This is because the actual equation of h bar divided by 2. However h bar has a value of h/2 pi, therefore giving you h/4 pi

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It is because of the size of the fluoride and chloride ion too. The fluoride ion is smaller than the chloride ion as size of an ion increases down a group. Therefore, the electrons are held more closely and hence, the bond is stronger.

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Isoelectronic means atoms or ions that have the same number of electrons. An example of this would be Na+, Mg2+

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After the 3D orbital is filled, it falls to a lower energy than the 4s orbital. Therefore, since electrons are first lost from the highest energy shell or valence shell first, the 4s orbital loses electrons before the 3D orbital.

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The double bond consists of two types of bonds, the pi bond and the sigma bond. The sigma bond is stronger than the pi bond which results in a shorter bond length. As for a triple bond, there are two pi bonds and one sigma bond, which results in an even shorter bond length.

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For Chemistry 14A, those are the only elements we need to know follow the expanded octet rule. However, any element in Period 3 or later can generally experience an expanded octet due to the presence of the additional d and f subshells that get filled at higher energy levels.

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Benzene has two possible resonant structures, with alternating double and single covalent bonds between Carbon atoms. On account of this variability in the density of the electron cloud, there is known to be a stable cloud of electrons on either side of the benzene molecule. Thus, this provides grea...

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You have to know that a higher negative charge means that there are more electrons added to the atom to achieve stability. There is greater electron-electron repulsion when electrons are added to the valence shell. As you move left to right across the periodic table, the atomic radius decreases. By ...

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Resonant structures show all the possible orientations the electrons can take within a molecule. All resonant structures are virtually the same. They exist only because of the electron density shifting.

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Cu and Cr do not follow the traditional Aufbau principle as half or fully filled d-orbitals are at a higher energy than s orbitals. This is done to reduce electron-electron repulsion within the orbital.

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Yes, this is due to electron shielding. Electron shielding results in a lower effective nuclear charge on the valence electrons and thus explains why valence electrons take part in chemical reactions.

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The electron will only absorb energy equal to the energy difference between two energy levels. Therefore if the energy is greater than the energy difference, the photon will not be absorbed unless the excess energy can be released in another way (eg. lattice vibration). However, assuming this is not...

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The Aufbau Principle states that the orbitals with the lower energy level get filled with electrons before the higher energy level. Thus, this gives us information about the electronic configuration of the atom.

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l indicates the azimuthal quantum number of an element that denotes the subshells the element contains;
l=0 signifies the s orbital (with a possible value of 0)
l=2 signifies the p orbital (with possible values of -1,0,1)
l=3 signifies the d orbital ( with possible values of -2, -1, 0, 1, 2)

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The answer for #13 would be C. Atomic absorption spectroscopy; Absorption line spectrum, as this question asks about absorption, and the process of finding the spectrum of the compound out is called Atomic absorption spectroscopy, and this produces an Absorption line spectrum. The answer for #14 wou...

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In 1m there are 1650763.73 wavelengths of krypton-86. There by dividing 1m by 1650762.72 wavelengths, the wavelength of each wave can be calculated to be 605.8nm. Thus, this falls under the visible spectrum. The energy can then be calculated by using the equation c=\nu \lambda , followed by the equa...

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The De Broglie cannot be used for light as light or photons are considered to massless, and thus any answer that you would get from that equation would be zero. The De Broglie equation can only be used for objects with a small mass and high frequency.

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The Balmer and Lyman series are series defined by the final position of the electron, after a photon is emitted. The Lyman series involve jumps to or from the ground state (n=1); the Balmer series (in which all the lines are in the visible region) corresponds to n=2.

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The threshold energy required to remove an electron from the metal surface varies from metal to metal. Each metal has a different threshold energy. To remove an electron from the metal surface, the energy of the photon hitting the metal surface has to be exactly equal to the difference of energy bet...

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No; you should only round your answer to the proper amount of significant figures at the end of the problem. You should never round off your intermediary calculations.

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You only have to do five problems out of the ones that Professor Lavelle selected, but my TA said it is highly beneficial to do most or even all the selected problems. I think about 1/8 problems on the tests are based off of the concepts from the homework.

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